In the evolution of wireless air interface standards, an objective has been optimizing for the best interest of carriers, such as maximizing the network capacity, or carrier's revenue. There are examples where such evolution has been achieved through sacrificing end user's interest, such as terminal's battery life. Examples include, 2G CDMA IS95 standard evolved into 2.5G IS2000, and 2G GSM/GPRS evolved into 3G W-CDMA/UMTS. In both cases the handset user's battery life decreased significantly.
On the other hand, although the air interface standards have been evolving with a goal of maximizing overall network capacity, in reality, the wireless network is not always operating in full load (or maximum capacity) all the time and at all the locations. Most of the time and/or at most locations, the load levels are lower than the full capacity, and the unused capacity is wasted.
One reason that IS95 and GSM/GPRS handsets have much longer talk time than 3G CDMA based handsets (IS2000 and UMTS) is because the latter uses continuous transmission. Their transmitter and/or receiver must be turned on for a high percentage of the time. Similar issues also appear in OFDM/OFDMA based standards, such as Wimax.